1. Field of the Invention and Related Art Statement
The present invention relates to a printing method and a printer for bar codes in which a variety of codes are formed by the combination of narrow lines and wide lines.
2. Discussion of the Background
Generally in the case of bar codes, many kinds of codes formed with the combination of narrow lines and wide lines are set and they are printed on sheets of printing paper by thermal printers.
As for printing methods there are two methods; one is a thermosensible method in which thermosensible paper is used for a printing medium and the other is an ink transcription method in which ink is transcribed through a printing ribbon on a printing medium of ordinary paper. In an ink transcription method a thermal transfer ink ribbon is used. Some printers are provided with stretching mechanisms for ribbons not to be slacken.
Even if any printing method is adopted, there are a plurality of standards in bar codes and in each standard the number of characters per unit dimension, the size of a narrow bar and the ratio between the sizes of a narrow bar and a wide bar are different. There are standard specifications and optional specifications in the kinds of bar codes. Standard specifications include
(a) JAN, UPC, EAN PA1 (b) NW-7 PA1 (c) CODE 39 PA1 (d) ITF etc., PA1 (e) CODE 128 PA1 (f) CODE 93 PA1 (g) MSI PA1 (h) others etc.
and optional specifications include
FIG. 12 (a), (b) and (c) show a printed example of a bar
code 1 wherein a line thermal head of 7.6/mm dot density is used
and narrow bars (NARROW) are 1 dot, 2 dots and 3 dots, and the ratio between the sizes of a narrow bar and a wide bar (WIDE) is 3 : 1. Usually on both ends of a bar code 1, guard bars 2 are disposed and there are margins 3 outside the guard bars 2.
When a bar code is printed by an ink transcription method using an ink ribbon, the ink ribbon can be locally shrunk by the influence of heat generated by a thermal head. In such a case, wrinkles occur in the ribbon and the ink once stuck on a sheet of printing paper re-adheres to the ribbon, a phenomenon called removableness, which degrades the printing quality of the bar code 1. Insufficient inking is apt to occur in both end parts of the bar code 1. It is caused by the fact that wrinkles are most likely to occur on the border between a printed region and a nonprinted region.